Numerous computer keyboards utilize a flexible sheet or layer of nonconductive material beneath the key caps in which the flexible sheet has molded dome portions at each key position to serve as a "return spring" to return a depressed key to it original undepressed condition. Examples as such flexible dome sheets are shown in several U.S. patents including U.S. Pat. No. 4,571,466 granted to Iida. A further example is illustrated in FIG. 1. A flexible keyboard dome switch layer or sheet 10 is illustrated in FIG. 1 having an alphanumeric layout with additional function keys and keypad keys. The keyboard layout is frequently referred to as a one-hundred and one key keyboard layout having one-hundred and one keyswitch positions 14. The keyswitch positions 14 are arranged in a plurality of parallel key rows 16a-16f. The sheet 10 has a base 18 that is normally supported on a rather rigid support plate or printed circuit board with a plurality of integral upstanding dome resilient bodies 20. The sheet 10 is molded from a flat sheet of resilient material with each dome body 20 being formed under heat and pressure within the mold cavity. Each dome body 20 has a cylindrical or circular-cross section, dome-shaped upstanding sidewall extending upward from the base 18 at each key position 14 for engaging a key cap structure to spring bias the key cap to an elevated condition in which the keyswitch is unactuated. Often the dome body has an actuating element formed integrally with the body that either directly or indirectly actuates the keyswitch when the key cap is depressed by the keyboard operator.
Although computer keyboards having flexible dome layers have become popular during the past 10 years, they are not with their disadvantages. Production quality molds are rather expensive to construct and as such are generally only justified when rather large volumes of dome sheets are required. Additionally, a separate mold is generally required for each different key layout, requiring the construction of a separate mold for each different keyboard layout. Moreover, the mold cycle time (time required to load an unmolded sheet into the mold, close the mold, open the mold, and to let the molded sheet cool) is not insignificant, limiting the cost effectiveness of resilient dome switch layers in keyboards as substitutes or alternatives to other types of key switch return spring structures.